Sites and Mobility of Lithium along the Li1+xTi2-xInx(PO4)3 (0 ≤ x ≤ 2) Series Deduced by XRD, NMR, and Impedance Spectroscopy.

The structure and Li conductivity has been investigated in the Li1+xTi2-xInx(PO4)3 (0 ≤ x ≤ 2) series prepared by the ceramic route at 900 °C. The XRD patterns of 0 ≤ x ≤ 0.2 samples show the presence of rhombohedral (S.G. R3̅c); those of 0.2 ≤ x ≤ 1 samples display both rhombohedral and orthorhombic (S.G. Pbca), and 1 ≤ x ≤ 2 samples exhibit only monoclinic (S.G. P21/n) phases. At intermediate compositions, the secondary LiTiPO5 phase was detected. The Rietveld analysis of XRD patterns was used to deduce unit-cell parameters, chemical composition, and percentage of phases. The amount of In3+, deduced from structural refinements of three phases, was confirmed by 31P MAS NMR spectroscopy. The Li mobility was investigated by 7Li MAS NMR and impedance spectroscopies. The Li conductivity increased with the Li content in rhombohedral but decreased in orthorhombic, increasing again in monoclinic samples. The maximum conductivity was obtained in the rhombohedral x = 0.2 sample (σb = 1.9 × 10-3 S·cm-1), with an activation energy Eb = 0.27 eV. In this composition, the overall Li conductivity was σov = 1.7 × 10-4 S·cm-1 and Eov = 0.32 eV, making this composition a potential solid electrolyte for all-solid-state batteries. Another maximum conductivity was detected in the monoclinic x ∼ 1.25 sample (σov = 1.4 × 10-5 S·cm-1), with an activation energy Eov = 0.39 eV. Structural models deduced with the Rietveld technique were used to analyze the conduction channels and justify the transport properties of different Li1+xTi2-x Inx(PO4)3 phases.

29Si Magic Angle Spinning Nuclear Magnetic Resonance, Fourier-Transform Infrared, and Monte Carlo Study of Synthetic Tetrasilicic Magnesium Mica Solid Solutions.

The parallel 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier-transform infrared study of synthetic micas made it possible to compare structural features of the tetrasilicic magnesium mica K(Mg2.5□0.5) Si4O10(OH)2 (TMM) and their K(Mg3)(Si3.5Mg0.5)O10(OH)2 (TMMA) and K(Mg3)(Si3.5Be0.5)O10(OH)2 (TMMB) derivatives. In the TMM mica, SiO4 tetrahedra are elongated in the plane ab and shortened along the c* direction with respect to those of the phlogopite (Phl) K(Mg3)(Si3Al)O10(OH)2. The substitution of Si4+ by R2+ (Mg2+ or Be2+) produces, besides the 29Si MAS NMR signal of Si (3Si) at -91.2 ppm, new components at -84.4 or -87.5 ppm that correspond to Si (2Si1Mg) or Si(2Si1Be) environments. Tetrahedral cation distributions in TMM/TMMA, TMM/TMMB solid solutions are investigated with respect to the TMM/Phl series by means of NMR and Monte Carlo simulations, concluding that divalent Mg2+ and Be2+ are further dispersed than trivalent Al3+ cations in tetrahedral sheets of micas. In three analyzed series, cation distributions display features between those of the homogeneous dispersion of charges of phlogopites and the maximum dispersion of charges of TMM derivatives. In three series, the location of charge deficits that compensate K+ cations changes from octahedral in TMM to tetrahedral sheets in phlogopite and TMMA and TMMB derivatives.

Hybrid Cements: Mechanical Properties, Microstructure and Radiological Behavior.

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic specimens in alkaline pastes was found to be valid. The variables involved in hybrid cement activation were shown to have no impact on specimen radioactive content. The powder samples, however, emanated 222Rn (a descendent of 226Ra), possibly due to the deformation taking place in fly ash structure during alkaline activation. Further research would be required to explain that finding.

Cation Miscibility and Lithium Mobility in NASICON Li1+xTi2-xScx(PO4)3 (0 ≤ x ≤ 0.5) Series: A Combined NMR and Impedance Study.

Rhombohedral NASICON compounds with general formula Li1+xTi2-xScx(PO4)3 (0 ≤ x ≤ 0.5) have been prepared using a conventional solid-state reaction and characterized by X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and impedance spectroscopy. The partial substitution of Ti4+ by Sc3+ and Li+ in pristine LiTi2(PO4)3 increases unit-cell dimensions and the number of charge carriers. In Sc-rich samples, the analysis of XRD data and 6Li/7Li, 31P, and 45Sc MAS NMR spectra confirms the presence of secondary LiScO2 and LiScP2O7 phases that reduce the amount of lithium incorporated in the NASICON phase. In samples with x < 0.3, electrostatic repulsions between Li ions located at M1 and M3 sites increase Li mobility. For x ≥ 0.3, ionic conductivity decreases because of secondary nonconducting phases formed at grain boundaries of the NASICON particles (core-shell structures). For x = 0.2, high bulk conductivity (2.5 × 10-3 S·cm-1) and low activation energy (Ea = 0.25 eV) measured at room temperature make Li1.2Ti1.8Sc0.2(PO4)3 one of the best lithium ionic conductors reported in the literature. In this material, the vacancy arrangement enhances Li conductivity.

Water-Free Proton Conduction in Discotic Pyridylpyrazolate-based Pt(II) and Pd(II) Metallomesogens.

In this work we report on water-free proton conductivity in liquid-crystal pyridylpyrazolate-based Pt(II) and Pd(II) complexes [M(pz(R(n,n)py))2] (pz(R(n,n)py) = 3-(3,5-dialkyloxyphenyl)-5-(pyridin-2-yl)pyrazolate, R(n,n) = C6H3(OCnH2n+1)2; n = 4, 12, 16, M = Pd; n = 12, M = Pt) with potential application as electrolyte materials in proton exchange membrane fuel cells. The columnar ordering of the complexes in the liquid-crystalline phase opens nanochannels, which are used for fast proton exchange as detected by impedance spectroscopy and NMR. The NMR spectra indicate that the proton conduction mechanism is associated with a novel C-H···N proton transfer, which persists above the clearing point of the material. The highest conductivity of ∼0.5 µS cm(-1) at 180 °C with an activation energy of 1.2 eV is found for the Pt(II) compound in the mesophase. The Pd(II) complexes with different chain length (n = 4, 12, and 16) show lower conductivity but smaller activation energies, in the range of 0.74-0.93 eV.

Synthesis and characterization of NaNiF3·3H2O: an unusual ordered variant of the ReO3 type.

A new hydrated sodium nickel fluoride with nominal composition NaNiF3·3H2O was synthesized using an aqueous solution route. Its structure was solved by means of ab initio methods from powder X-ray diffraction and neutron diffraction data. NaNiF3·3H2O crystallizes in the cubic crystal system, space group Pn3̅ with a = 7.91968(4) Å. The framework, derived from the ReO3 structure type, is built from NaX6 and NiX6 (X = O, F) corner-shared octahedra, in which F and O atoms are randomly distributed on a single anion site. The 2a × 2a × 2a superstructure arises from the strict alternate three-dimensional linking of NaX6 and NiX6 octahedra together with the simultaneous tilts of the octahedra from the cube axis (φ = 31.1°), with a significant participation of hydrogen bonding. NaNiF3·3H2O corresponds to a fully cation-ordered variant of the In(OH)3 structure, easily recognizable when formulated as NaNi(XH)6 (X = O, F). It constitutes one of the rare examples for the a(+)a(+)a(+) tilting scheme with 1:1 cation ordering in perovskite-related compounds. The Curie-like magnetic behavior well-reflects the isolated paramagnetic Ni(2+) centers without worth mentioning interactions. While X-ray and neutron diffraction data evidence Na/Ni order in combination with O/F disorder as a main feature of this fluoride, results from Raman and magic-angle spinning NMR spectroscopies support the existence of specific anion arrangements in isolated square windows identified in structural refinements. In particular, formation of water molecules derives from unfavorable FH bond formation.

Self-diffusion in polycrystalline Li1+x Ti2-x Al x (PO4)3 (0.2 ≤ x ≤ 0.4) samples followed by 7Li PFG (pulse field gradient) NMR spectroscopy.

Short and long range lithium motions in powder Li1+x Ti2-x Al x (PO4)3 (LTAP) NASICON compounds prepared by ceramic (x = 0.2 and 0.4) and sol-gel (x = 0.3 and 0.4) routes are discussed. ND diffraction and MAS-NMR spectroscopy were previously used to investigate structural features of these compounds. In particular, Fourier map differences showed that the amount of Li atoms allocated at M3 increases at the expense of M1 sites when the Li content increases. In this work, PFG-NMR results show that diffusion coefficients rise with the amount of lithium and temperature. The restricted diffusion inside NASICON particles is compared with "free" diffusion processes. At 300 K, diffusion coefficients D PFG ∼ 5 × 10-12 m2 s-1 have been deduced in ceramic x = 0.2 and 0.4 samples, decreasing with diffusion time Δ used in PFG experiments. In sol-gel samples, diffusion coefficients are near those of ceramic samples, but decrease faster with diffusion Δ times, as a consequence of the Li confinement inside sub-micrometric crystallites. The NMR spin-echo signal displays minima at specific q(γgδ) values that are related to the crystallite size. From R dif ∼ q m -1 distances, calculated from the position of minima, and from diffusion coefficients deduced for high Δ values, the mean crystallite size was estimated. Finally, from the temperature dependence of conductivity and diffusion coefficients, the activation energy and charge carriers concentrations were determined.

Electrical and Structural Properties of Li1.3Al0.3Ti1.7(PO4)3-Based Ceramics Prepared with the Addition of Li4SiO4.

The currently studied materials considered as potential candidates to be solid electrolytes for Li-ion batteries usually suffer from low total ionic conductivity. One of them, the NASICON-type ceramic of the chemical formula Li1.3Al0.3Ti1.7(PO4)3, seems to be an appropriate material for the modification of its electrical properties due to its high bulk ionic conductivity of the order of 10-3 S∙cm-1. For this purpose, we propose an approach concerning modifying the grain boundary composition towards the higher conducting one. To achieve this goal, Li4SiO4 was selected and added to the LATP base matrix to support Li+ diffusion between the grains. The properties of the Li1.3Al0.3Ti1.7(PO4)3-xLi4SiO4 (0.02 ≤ x ≤ 0.1) system were studied by means of high-temperature X-ray diffractometry (HTXRD); 6Li, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); thermogravimetry (TG); scanning electron microscopy (SEM); and impedance spectroscopy (IS) techniques. Referring to the experimental results, the Li4SiO4 additive material leads to the improvement of the electrical properties and the value of the total ionic conductivity exceeds 10-4 S∙cm-1 in most studied cases. The factors affecting the enhancement of the total ionic conductivity are discussed. The highest value of σtot = 1.4 × 10-4 S∙cm-1 has been obtained for LATP-0.1LSO material sintered at 1000 °C for 6 h.

New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash.

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

The structure of kaliophilite KAlSiO4, a long-lasting crystallographic problem.

Kaliophilite is a feldspathoid mineral found in two Italian magmatic provinces and represents one of the 12 known phases with composition close to KAlSiO4. Despite its apparently simple formula, the structure of this mineral revealed extremely complex and resisted structure solution for more than a century. Samples from the Vesuvius-Monte Somma and Alban Hills volcanic areas were analyzed through a multi-technique approach, and finally the crystal structure of kaliophilite was solved using 3D electron diffraction and refined against X-ray diffraction data of a twinned crystal. Results were also ascertained by the Rietveld method using synchrotron powder intensities. It was found that kaliophilite crystallizes in space group P3 with unit-cell parameters a = 27.0597 (16), c = 8.5587 (6) Å, V = 5427.3 (7) Å3 and Z = 54. The kaliophilite framework is a variant of the tridymite topology, with alternating SiO4 and AlO4 tetrahedra forming sheets of six-membered rings (63 nets), which are connected along [001] by sharing the apical oxygen atoms. Considering the up (U) and down (D) orientations of the linking vertex, kaliophilite is the first framework that contains three different ring topologies: nine (1-3-5) (UDUDUD) rings, six (1-2-3) (UUUDDD) rings and twelve (1-2-4) (UUDUDD) rings. This results in a relatively open (19.9 tetrahedra nm-3) channel system with multiple connections between the double six-ring cavities. Such a framework requires a surprisingly large unit cell, 27 times larger than the cell of kalsilite, the simplest phase with the same composition. The occurrence of some Na for K substitution (3-10%) may be related to the characteristic structural features of kaliophilite. Micro-twinning, pseudo-symmetries and anisotropic hkl-dependent peak broadening were also detected, and they may account for the elusive character of the kaliophilite crystal structure.

Insight into ramsdellite LI(2)Ti(3)O(7) and its proton-exchange derivative.

Despite being proven to be a good lithium-ion conductor 30 years ago, the crystal structure of the ramsdellite-like Li(2)Ti(3)O(7) has remained uncertain, with two potential models for locating the lithium ions in the structure. Although the model presently accepted states that both lithium and titanium occupy the octahedral sites in the framework, evidence against this model are provided by (6)Li and (7)Li MAS NMR spectroscopy. Thus, about 14% of these octahedral positions are empty since no lithium in octahedral coordination is present in the material. When Li(2)Ti(3)O(7)-ramsdellite is treated with nitric acid a complete exchange of lithium by protons is produced to yield H(2)Ti(3)O(7). The crystal structure of this proton-exchanged ramsdellite has been re-examined combining X-ray diffraction (XRD), neutron powder diffraction (NPD), and spectroscopic ((1)H and (7)Li MAS NMR) techniques. Two kinds of protons are present in this material with different acidity because of the local environments of oxygen atoms to which protons are bonded, namely, low acidic protons strongly bonded to highly charged oxygen atoms (coordinated to two Ti(4+) and a vacancy); and protons linked to low charged oxygen atoms (bonded to three Ti(4+) ions) which will display a more acidic behavior. H(2)Ti(3)O(7) absorbs water; proton mobility is enhanced by the presence of absorbed water, giving rise to a large improvement of its electrical conductivity in wet atmospheres. Thus, it seems that water molecules enter the tunnels in the structure providing a vehicle mechanism for proton diffusion.

Microstructural and Mechanical Properties of Alkali Activated Colombian Raw Materials.

Microstructural and mechanical properties of alkali activated binders based on blends of Colombian granulated blast furnace slag (GBFS) and fly ash (FA) were investigated. The synthesis of alkali activated binders was conducted at 85 °C for 24 h with different slag/fly ash ratios (100:0, 80:20, 60:40, 40:60, 20:80, and 0:100). Mineralogical and microstructural characterization was carried out by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) and Nuclear magnetic resonance (NMR). Mechanical properties were evaluated through the compressive strength, modulus of elasticity and Poisson's ratio. The results show that two different reaction products were detected in the slag/fly ash mixtures, a calcium silicate hydrate with Al in its structure (C-A-S-H gel) and a sodium aluminosilicate hydrate (N-A-S-H gel) with higher number of polymerized species and low content in Ca. It was found that with the increase of the amount of added slag, the amount of C-A-S-H gel increased and the amount of N-A-S-H gel decreased. The matrix was more dense and compact with almost absence of pores. The predominance of slag affected positively the compressive strength, Young's modulus and Poisson's ratio, with 80% slag and 20% fly ash concrete being the best mechanical performance blend.

Insight into the channel ion distribution and influence on the lithium insertion properties of hexatitanates A2Ti6O13 (A = Na, Li, H) as candidates for anode materials in lithium-ion batteries.

Li(2)Ti(6)O(13) and H(2)Ti(6)O(13) were easily synthesized from Na(2)Ti(6)O(13) by successive Na(+)-Li(+)-H(+) ion exchange. The crystal structures of Na(2)Ti(6)O(13), Li(2)Ti(6)O(13) and H(2)Ti(6)O(13) were investigated using neutron powder diffraction. Monovalent A(+) cations (Na, Li and H) have been located using difference Fourier analysis. Although monoclinic lattice parameters (space group C2/m) of the three titanates remain almost unchanged with retention of the basic [Ti(6)O(13)(2-)] network, monovalent Na, Li and H cations occupy different sites in the tunnel space. By comparing the structural details concerning the A(+) oxygen coordination, i.e. NaO(8) square prismatic coordination, LiO(4) square planar coordination and covalently bond H atoms, with results from (23)Na, (7)Li and (1)H NMR spectroscopy we were able to obtain a more detailed insight into the respective local distortions and anharmonic motions. We were able to show that the site that the A(+) cation occupies in the hexatitanate channel structure strongly influences the lithium insertion properties of these compounds and therefore their usefulness as electrode materials for energy storage.

Structural characterization and NMR study of NaNbWO(6) and its proton-exchanged derivatives.

The structural characterization of NaNbWO(6), prepared by the ceramic route, has been performed. Electron diffraction has shown the presence of two related phases in a 1:1 ratio, whose lattice parameters correspond to those of the well-known tetragonal tungsten bronzes (TTB) and those of a monoclinically distorted phase. In addition to basic unit cells, the morphology of the two phases has been found to be similar, but they present a slight difference in the W/Nb ratio. (1)H and (23)Na magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectra of NaNbWO(6) and its proton-exchanged derivatives have been interpreted on the basis of the ideal TTB structure. The average structure and the morphology remain unchanged in Na(1-x)H(x)NbWO(6) derivatives. (1)H and (23)Na MAS-NMR spectroscopies have been used to monitor changes produced during exchange processes. It has been shown that the exchange of Na ions is mainly produced, but not exclusively, at tetragonal channels. However, a large amount of Na ions at the pentagonal channels do not exchange with protons, suggesting that these ions are needed to stabilize the TTB-like structure. A tentative distribution of sodium ions in the most-exchanged oxide, deduced from NMR results, approximately (Na(0.46))(p)(Na(0.08))(s)H(0.46)NbWO(6), has been proposed. NMR spectra of Na(1-x)H(x)NbWO(6) indicate that two different OH groups are formed upon exchanging. The study of samples hydrated with D(2)O allowed us to conclude that deuterons of adsorbed water exchange with protons of the two OH groups. The proton-deuteron exchange is slow at room temperature but is strongly enhanced at 90 degrees C. This observation relates to the proton conductivity displayed by exchanged products under a humid atmosphere.

Layered microporous tin(IV) bisphosphonates.

This article reports the hydrothermal synthesis and characterization of two new series of porous tin(IV) phosphonophenoxyphenylphosphonates with controlled pore size distributions, using as precursor the 4-(4'-phosphonophenoxy)phenyl phosphonic acid, [H2O3P-C6H4]2-O. Supermicroporous solids (S(BET), 300-400 m2 g(-1)) were obtained employing n-alcohol (C1-C6)-water mixtures (solvents ratio 1 : 1), in the presence of hydrofluoric acid. X-Ray powder diffraction shows that these compounds are semi-crystalline and the local environments around the phosphorus and tin elements have been studied by 31P and 119Sn MAS-NMR spectroscopy, respectively. The microstructure (particle sizes and shapes) of these phosphonates has been analyzed by scanning and transmission electron microscopy. This study shows that the microstructures of single-ligand (for instance tin(IV) phenylphosphonate) and cross-linked tin(IV) bisphosphonates are different. Tin(IV) phenylphosphonate crystallizes as micron-sized spheres, theta approximately 1-2 microm, formed by the aggregation of nanospheres, whereas tin(IV) bisphosphonates crystallize as microparticles larger than 20 microm. The textural properties of these porous solids were characterized by N2 and CO2 sorption isotherms. The key result of this work is that maxima of pore size distributions smoothly shift from 12 to 16 angstroms upon increasing the chain length of the alcohol. The microporosity of tin(IV) bisphosphonates is compatible with a double role played by the phosphonate groups acting as a pillar between adjacent layers and as a component of the hybrid organic-inorganic layers.